Common lamination component for accommodating multiple conductor geometries in an electric machine

ABSTRACT

Rectangular conductor wires ( 38 ) are often used in alternator applications requiring a high slot fill to maximize output and efficiency. However for lower output and efficiency applications, round conductor ( 40 ) wire may increase cost competiveness in these alternators. A common lamination for a core ( 110 ) alternatively accommodates both rectangular conductor wires ( 38 ) and round conductor wires ( 40 ) for different applications without any other component changes. The lamina has a slot ( 112 ) that aligns round wire ( 40 ) in a single row within the slot and provides a predetermined clearance from the slot opening ( 126 ). A stator core ( 110 ) formed from these laminae has a relatively high slot fill factor when wound with the round wire ( 40 ). The same stator core ( 110 ) can be alternatively wound with square wire ( 38 ) to increase the slot fill factor even higher. The common lamination results in two stator configurations: a high slot fill version (round wire) and a very high slot fill version (square wire).

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication No. 62/323,313, filed Apr. 15, 2016, the contents of whichare incorporated herein by reference.

FIELD

This application relates to the field of electric machines, andparticularly to the accommodation of multiple conductor geometries inrotary electric machines.

BACKGROUND

Rotary electric machines operate by exploiting the interaction of themagnetic fields of a rotor and a stator rotating relative to oneanother. In a common application, the rotor is disposed within androtatable relative to the stator. The rotor is typically fixed to ashaft mounted for rotation centrally by bearings disposed in a casingthat surrounds the stator. These machines include a configuration ofinsulated wire coils or windings in the stator, which are distributedabout the stator central axis. The windings are typically arranged in aprogressive sequence to define different electrical phases. The statorwindings are typically wound around ferromagnetic poles of the statorcore to enhance the strength of the stator's magnetic field. The statorpoles generally are tooth-like cross sections that are usuallyrectangular or trapezoidal, and typically defined by slots in the statorcore.

In a polyphase electric motor, flowing current of different phasesthrough a progressive sequence of wire windings in the stator generatesrotating magnetic fields in the stator, which impart electromechanicaltorque to the rotor and its shaft. Conversely, in a polyphase electricgenerator or alternator, externally forced rotation of the shaft androtor imparts rotation to magnetic fields that induce current flows inthe stator windings.

The stator core may be formed by a stack of interlocked, ferrouslaminae, which are typically formed from electrical sheet steel. Eachlamina has a central hole with the holes of all the laminae beingaligned in the lamina stack to form a stator core central bore having acentral axis. Thus, the stator core may be a unitary annular member withits central bore defining a radial internal bore face that is generallycylindrical and centered about the central axis. The radial internalbore face is provided with the generally axially extending, elongateslots formed by aligned, notched portions of the lamina holes thatdefine the stator poles. The stator slots pass axially through thelamina stack adjacent the central bore since they extend over the entireaxial length of the lamina stack and are open radially on an internalside and the two opposite axial ends.

The slots formed by the lamina stack typically lie in planes thatintersect along and contain the stator central axis, but the slots canalso be inclined with respect to central axis. The stator slots aretypically distributed at an even pitch about the stator central axis.Relative to the stator, radial and axial directions mentioned herein arerespective to the stator central axis, and the stator slots generallyextend radially from the central bore face into the stator core andaxially along the bore length. Thus, each stator core slot has agenerally axial length dimension extending along the length of thestator core bore, a width dimension extending circumferentially aboutthe central axis between a pair of adjacent stator core teeth, and aradial depth dimension extending between the slot opening proximate thestator core central bore and the slot bottom.

Elongate electrical conductors that define the stator coil windings aredisposed in and extend along the stator slots. By virtue of theconductors being routed through the stator slots, they are wrapped aboutthe stator poles. Typically, a stator slot insulator insert is locatedbetween the conductors and the walls of the stator slots to ensureelectrical isolation of the stator windings from the stator core.Typically, the insulator insert is formed of a flexible, electricallyinsulative sheet material such as a paper or plastic that is insertedinto the slot before a conductor is installed therein. The sheetmaterial forms an electrically insulative layer between the conductorsand their respective stator slot.

In a polyphase rotary electric machine, the stator coil windings includea plurality (typically three, five, six, or seven) of different phasewindings each formed of elongate electrical conductor material such as acopper magnet wire or bar. The conductor cross-section is typicallycircular or rectangular (including square), or oval. Round wire ofconventional sizes may be used for the conductors. Optionally, thick barconductors can be used for making a wire coil with a designedcurrent-carrying capacity requiring fewer turns than is possible withsmaller sized round wire.

Each stator slot may accommodate multiple, small diameter wire segmentsthat are wound in bulk and rather randomly oriented and located, andtypically cross over each other, within the slot. Examples of suchwindings are well-known to those having ordinary skill in the relevantart. Alternatively, the stator slots may have a depth and/or width thatis a multiple of the cross-sectional dimension of the conductor, in theslot's radial and/or circumferential direction. In the example of athree-phase stator, multiple electrical conductor segments may be housedwithin each of the stator slots with the electrical conductors arrangedin a predetermined winding pattern to form the stator winding.

The particular winding patterns of stator windings can vary considerablybetween different machine designs and include, for example,standard-wind configurations, S-wind configurations, or segmentedconductor configurations. S-wind configurations typically include acontinuous length of wire that is wound in an out of the various slotsof the stator, where end loops connect a in-slot portions in one layerto an in-slot portion in the same layer, to form a complete winding. Thewire includes relatively straight lengths that are positioned within theslots of the core portion and curved lengths that extend between in-slotportions at the ends of the core portion. Similarly, in a segmentedwinding configuration, the windings typically comprise a plurality ofsegmented conductors which include in-slot portions and ends that areconnected together. The in-slot portions of the conductors arepositioned in the stator slots, and the ends of the conductors areconnected to form windings for the electric machine.

It is known that increasing the fill of a conductor material in a statorslot improves both the performance and efficiency of an electricalmachine. Such high slot fill stators often include rectangular shapedconductors that are aligned single file in one radial row in each slotand that fit closely to the width of the insulated, rectangular shapedcore slots. The use of rectangular wires in high slot fill statorapplications can, however, increase the complexity of placing thewinding in the stator. In addition, the cost per kilogram of rectangularwire is significantly more than the cost per kilogram of round wire.Thus, for applications requiring less output and efficiency, the use ofround wire instead of rectangular or square wire in the same electricalmachine could provide significant cost savings by taking advantage ofexisting technologies, such as current S-wind technology. However,existing high slot fill applications incorporate stator slot geometriesthat often only accept rectangular wire.

Accordingly, it would be advantageous to provide a common laminationcomponent for electric machines which alternatively accommodates bothrectangular or square wire and round wire for different applicationswithout the need for any other component changes in the electricalmachine.

SUMMARY

A stator core for an electric machine in one embodiment includes a corebody having a plurality of teeth, adjacent teeth of the plurality ofteeth defining respective slots in the core body, each slot having aslot depth in a respective direction along which the teeth extend fromthe core body and a slot width in a respective direction along which theteeth are spaced circumferentially from each other, the core body has aconfiguration in which a plurality of elongate wire segments having around cross section are arranged in single file within each slot, theround cross section having a diameter that approximates the slot width,the slot depth has a range defined by the equation(N*Ø)+0.2≦D_(C)′≦(N+1)*Ø where N equals the number of the wire segmentsin the slot and θ equals the diameter of the second wire segments.

Two stator core assemblies for respective electric machines in oneembodiment includes a first stator core and a second stator core that isidentical to the first stator core, each stator core having a pluralityof teeth with adjacent teeth of the plurality of teeth definingrespective slots, the first stator core has a first plurality ofelongate wire segments arranged in single file within in each slot, thefirst wire segments having a rectangular cross section, and the secondstator core has a second plurality of elongate wire segments arranged insingle file within each slot, the second wires segments having a roundcross section.

A method of producing a plurality of stator assemblies in one embodimentincludes forming a plurality of identical cores, each core having aplurality of teeth, adjacent teeth of the plurality of teeth definingrespective slots in the core body, winding a first core of the pluralityof cores with a first plurality of elongate wire segments, the firstwire segments having a rectangular cross section and are arranged insingle file within in each slot, the rectangular cross section having across-sectional dimension that approximates a slot width of the slot,winding a second core of the plurality of cores with a second pluralityof elongate wire segments, the second wires segments having a roundcross section and are arranged in single file within each slot, theround cross section having a diameter that approximates the slot width,the wound first core has a first slot fill factor and the wound secondcore has a second slot fill factor, the second slot fill factor within10 percent of the first slot fill factor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a perspective view of a high slot fill core of a prior artelectric machine;

FIG. 2 shows a cross-sectional view of a portion of the core of FIG. 1with at least one slot of the core including a plurality of rectangularconductors;

FIG. 3 shows an enlarged view of the slot of FIG. 2 illustrating thefeatures of the slot and the rectangular conductors in more detail;

FIG. 4 shows the core of FIG. 2 overlaid with round conductors toillustrate the incompatibility of the core to alternatively accommodateboth rectangular and round conductors;

FIG. 5 shows a cross-sectional portion of a core in accordance with thepresent invention with at least one slot of the core including aplurality of round conductors;

FIG. 6 shows enlarged view of the slot of FIG. 5 illustrating thefeatures of the slot and the round conductors in more detail;

FIG. 7 shows an overlay of the core of FIG. 2 and the core of FIG. 5with a bottom of the slots of the core of FIG. 2 shown in phantom lines;and

FIG. 8 shows a flow diagram of a method for producing a first coreassembly with rectangular conductors and second core assembly with roundconductors using the core of FIG. 5.

DETAILED DESCRIPTION

FIGS. 1 and 2 depict a prior art stator core 10 for use in a three-phaserotary electric machine. The core 10 has a core body 11 that includes anumber of core slots 12 arranged about a central axis 14 with each ofthe core slots 12 associated with one of the three current phases. Thisassociation progressively repeats itself in sequence around acircumferential inner surface 16 of the core 10, which defines asubstantially cylindrical bore 18 through the core 10. The core slots 12extend in a direction, indicated by an arrow 13, parallel to the centralaxis 14 of the core 10 between a first end 15 and a second end 17thereof. As used herein, an “axially upward direction” is defined asmoving toward the first end 15 of the core 10 and an “axially downwarddirection” is defined as moving toward the second end 17 of the core 10.

The core slots 12 are equally spaced around the circumferential innersurface 16 of the stator core 10 and respective inner surfaces 19 of thecore slots 12 are substantially parallel to the central axis 14. Thecore slots 12 have a depth D_(C) along a radial axis, indicated by anarrow 23, and are configured to receive a stator winding, discussed inmore detail below. As used herein, a “radial inward direction” isdefined as moving towards the central axis 14 of the core 10 and a“radial outward direction” is defined as moving away from the centralaxis 14.

The core 10 is formed of a stack of aligned, interconnected electricalsteel laminae, which define the circumferential inner surface 16 and thecore slots 12. The following features described with reference to the“core” or “core body” also describe features of individual lamina sincethe stack of laminae forms the core. Similarly, figures of the presentapplication that depict cross-sections of the “core” or “core body” canbe interpreted as depicting cross-sections of individual lamina. Thecore slots 12 are separated from one another by stator poles or teeth 20formed by the lamina stack. As viewed axially along arrow 13, thelongitudinal inner surfaces 19 of the core slots 12 are generallyU-shaped with approximately parallel sides 22, 24. The core slot sides22, 24 extend in the radial outward direction from a slot opening 26 inthe circumferential inner surface 16. As best shown in FIG. 3, the depthD_(C) of each core slot 12 extends from the slot opening 26 at thecircumferential inner surface 16 to a core slot bottom 28 that is spacedin the radial outward direction from the slot opening 26.

With reference to FIGS. 2 and 3, the core slots 12 are each fitted withrespective insulation sleeves 21 that electrically insulate one or moreelongate segments of copper magnet wire conductors 38 a-h positioned inthe core slots 12 from the core 10. The wire conductors 38 a-h shown inFIGS. 2 and 3 each have a rectangular cross-sectional shape with alength L_(RCS) extending substantially parallel to the radial axis 23and a width W_(RCS) extending substantially perpendicular to the radialaxis 23 between the parallel sides 22, 24. The cross-sectional area ofeach of the rectangular conductors 38 a-h is substantially equal. Therectangular conductors 38 a-h are aligned in a single row by therespective parallel sides 22, 24 of the core slots 12. As shown, it iscommon that the rectangular shaped conductors may include radii on thecorners intermediate two adjacent edges.

FIG. 3 shows an enlarged cross-sectional view of one of the core slots12 of the core 10 with eight rectangular conductors 38 a-h positionedtherein. The rectangular conductors 38 a-h may be positioned in anyconfiguration, including S-wind or segmented conductor configurations.In the configuration shown, each conductor 38 a-h is separated fromneighboring conductors in the core slot 12 by at least one insulationlayer 30 and from the core 10 by the insulation sleeve 21. Theinsulation layer 30 and the insulation sleeve 21 each have asubstantially uniform thickness. As used herein, “substantially uniformthickness” means a thickness in which deviations across integralsurfaces of an element from which the thickness is measured areminimized by known manufacturing methods. The length L_(RCS) and thewidth W_(RCS) of each the rectangular conductors 38 a-h referred toherein includes the thickness of the insulation layer 30. As shown inFIG. 3, the insulation sleeve 21 is positioned along the parallel sides22, 24 and the core slot bottom 28 so as to substantially surround theconductors 38 a-h in each of the slots 12 and thus defines a sleeve slot32 with a sleeve slot width W_(S) and a sleeve slot depth D_(S).

The sleeve slot width W_(S) at the slot openings 26 is slightly largerthan the width W_(RCS) of the rectangular conductors 38 a-h so as topermit the conductors 38 a-h to be inserted radially into the core slots12. The circumferential spacing between the adjacent teeth 20 may beconsistent along the depth D_(C) or the circumferential spacing maywiden slightly in the radial outward direction from the opening 26 to awidth W_(C) of the core slot 12 defined between the interfacing parallelsides 22, 24 of the circumferentially adjacent teeth 20. The statorwinding may be prepared using any variation of a conventional techniquesuitable for rectangular wire, and the rectangular conductors 38 a-h areinserted either individually or as a group into their respective coreslot 12 through its opening 26.

When viewed along a cross-sectional plane situated perpendicular to thecentral axis 14, each core slot 12 and sleeve slot 32, and the commonopening 26 thereto are centrally positioned about a slot radialcenterline 34 (FIG. 2). The difference in the core slot width W_(C) andthe sleeve slot width W_(S) is substantially equivalent to twice thethickness t (i.e., 2t) of the insulation sleeve 21 that lines the coreslot 12 and defines the interior of the sleeve slot 32. The insulationsleeve 21 is a known, flexible, dielectric material layer having thermalproperties suitable for conductively transferring heat between therectangular conductors 38 a-h and the core 10. As mentioned above, thesleeve 21 may be made of plastic or paper sheeting, for example. Asshown, each sleeve 21 extends continually along the perimeter of itsrespective core slot 12 and terminates at the circumferential innersurface 16.

The core slot width W_(C) and the insulation sleeve thickness t are suchas to allow unrestricted radial insertion of the rectangular conductors38 a-h into each core slot 12, between the slot walls defined by theinterfacing, parallel surface portions of its respective insulationsleeve 21. Thus, W_(S)=Wc−2t, and approximates the width W_(RCS) of therectangular conductors 38 a-h. There is typically a clearance of, forexample, from about 0.1 to 0.8 mm between the sleeve slot width Ws andthe width W_(RCS) of the rectangular conductors 38 a-h, the clearancebeing comparatively much smaller than the width W_(RCS) of therectangular conductors 38 a-h. In the embodiment depicted in FIGS. 2 and3, the insulation sleeve thickness t is about 0.125 mm and the core slotwidth W_(C) is about 2 mm such that sleeve slot width is 1.75 mm (2mm−(2*0.125 mm)). A rectangular conductor with a width W_(RCS) of about1.6 mm will have approximately 0.15 mm of clearance (1.75 mm-1.6 mm)between the parallel walls of the insulation sleeve 21. Thus, a singlefile arrangement of the rectangular conductors 38 a-h is maintainedalong the depth D_(S) of the sleeve slot 32 with the surfaces of thearranged rectangular conductors 38 a-h extending parallel with the widthW_(RCS) of the conductors in abutment with one another.

One issue with the core 10 depicted in FIGS. 1-3 is that the core slots12 are specifically configured to accept a specific number ofrectangular wire conductors to achieve a desired performancecharacteristic. This limitation is acceptable for some applications ofS-wind electrical machines since rectangular wire is typically used forhigh slot fill applications in order to achieve maximized output andefficiency from the machine. However, there are many applicationsrequiring lower output and efficiency in which round wire could be usedinstead of rectangular or square wire in order to take advantage of costsavings associated with use of common S-wind technology and laminationdesign.

There are numerous design considerations in standardizing a laminationslot design that alternatively accommodates both rectangular wires andround wires. For instance, round wire can be desirable over square wiresas it is much easier to insulate and therefore significantly lessexpensive to manufacture. As is known, square wire can be desirable overround wire in some applications because the cross-sectional area ishigher and, therefore, the slot fill is higher, which improvesperformance and efficiency while lowering stator temperature. Alamination with a slot width that is too wide is not desirable becausethe teeth will be thin and become easily saturated with flux. Alamination with a slot with that is too narrow is not desirable becausethe wire will become too thin and the current density of the wire willbe too high.

It has been determined that a desirable number of wires per slot is fiveto seven. However, windings with odd numbers of wires can be difficultto manufacture, so a particularly desirable number of wires per slot issix. For a 12V system, the equation V=N*d(phi)/d(t), where V=inducedvoltage, N=number of electrical turns, phi=magnetic flux, and t=time,suggests that six electrical turns may be an excessive number of turnsfor an electrical machine. Moreover, the rotor poles are typicallytwelve to sixteen poles due to manufacturing limitations. As is known,the number of poles and the surface linear speed of the rotor determined(phi)/d(t). Thus, to achieve the proper V for a 12V system, the numberof poles times the number of turns for a high slot fill wye-woundelectrical machine is typically around forty-eight, and the number ofelectrical turns is typically three or four. To achieve three or fourelectrical turns with a six wire-in-a-slot stator, the winding could bebifilar resulting in three turns, or the winding could bedelta-connected, resulting in three and one-half effective-wye turnssince delta effective wye turns equals turns/1.734.

It has additionally been determined that for a six wire-in-a-slot statorwith round wires, it is desirable to have about a 0.5 mm clearance fromthe circumferential inner surface 16 to the innermost conductor in theradial outward direction (i.e., rectangular conductor 38 a in FIGS. 2and 3). FIG. 4 depicts the core 10 of FIG. 2 overlaid with six roundconductors 40 a-f in the sleeve slot 32. For clarity, the rectangularconductors 38 a-h are illustrated using solid lines while the roundconductors are illustrated using dashed lines. The round conductors 40a-f each have a diameter Ø that is approximately equal to the widthW_(RCS) of the rectangular conductors 38 a-h. As used herein, a firstdimension that is “approximately equal to” or that “approximates” asecond dimension means the first dimension is within a narrowdimensional range measured from the second dimension. For example, around conductor 40 a-f with a diameter Ø of 2.0 mm is not approximatelyequal to a rectangular conductor 38 a-h with a width W_(RCS) of 1.6 mm,whereas a round conductor 40 a-f with a diameter Ø of 1.575 mm isapproximately equal to a rectangular conductor 38 a-h with a widthW_(RCS) of 1.6 mm. As is shown in FIG. 4, the innermost round conductor40 a has no clearance from circumferential inner face 16 in the radialoutward direction. Instead, the innermost round conductor 40 a extendsin the radial inward direction from the circumferential inner face 16.Thus, the slot design of the prior art core 10 does not sufficientlyaccommodate both rectangular wires and round wires in alternativeapplications under the aforementioned preferred conditions.

FIGS. 5 and 6 show a core 110 for use in a three-phase electricalmachine and configured to accept both rectangular conductors (i.e., 38a-h shown in FIGS. 2 and 3) and round conductors 40 a-f in alternativeapplications. The core wound with rectangular conductors may sometimesbe referred to herein as a “first configuration”, while the core woundwith round conductors may sometimes be referred to herein as a “secondconfiguration” although the structure of the core is identical in boththe first and second configurations. The core 110 also has the advantagethat a desired clearance between the circumferential inner surface 16and the innermost conductor (i.e., rectangular conductor 38 a in FIGS. 2and 3 and round conductor 40 a in FIGS. 5 and 6) results with eitherconductor geometry. In FIGS. 5 and 6, elements of the core 110 that aresimilar to those of the core 10 of FIGS. 1-4 are identified with likenumerals whereas new or changed elements are identified with a singleprime symbol or by incrementing the prior reference number by 100. Asused hereafter, the terms “rectangular conductor”, “rectangular wire”,or the like refer to a conductor with a rectangular, non-squarecross-sectional geometry when viewed along a cross-sectional planesituated perpendicular to the central axis 14 of the core 110.

The core 110 has a core body 111 that includes a number of core slots112 arranged about the central axis 14 with each of the core slots 112associated with one of the three current phases. This associationprogressively repeats itself in sequence around a circumferential innersurface 16 of the core 110, which defines a substantially cylindricalbore 18 through the core 10. The core slots 112 extend parallel to thecentral axis 14 of the core 110 between the first end 15 and the secondend 17 thereof. The core slots 112 are equally spaced around thecircumferential inner surface 16 of the stator core 110 and aresubstantially parallel to the central axis 14. The core slots 112 have adepth D_(C)′ (FIG. 6) along the radial axis 23 (FIG. 1).

The core 110 in the illustrated embodiment is formed of a stack ofaligned, interconnected electrical steel laminae, which define thecircumferential inner surface 16 and the core slots 112. The core inother embodiments can be formed in any other known manner. The followingfeatures described with reference to the “core” or “core body” alsodescribe features of individual lamina since the stack of laminae formsthe core 110. The core slots 112 are separated from one another bystator poles or teeth 120 formed by the lamina stack. As viewed axiallyalong the arrow 13 (FIG. 1), the longitudinal inner surfaces 119 of thecore slots 112 are generally U-shaped with approximately parallel sides122, 124. The core slot sides 122, 124 extend in the radial outwarddirection from the slot opening 126 in the circumferential inner surface16. As best shown in FIG. 6, the depth D_(C)′ of each core slot 112extends from the slot opening 126 at the circumferential inner surface16 to a core slot bottom 128 that is spaced in the radial outwarddirection from the slot opening 126.

The core slots 112 are each fitted with respective insulation sleeves121 that electrically insulate the round conductors 40 a-f positioned inthe core slots 112 from the core 110. As discussed with reference toFIG. 4, the diameter Ø of the round conductors 40 a-f is approximatelyequal to the width W_(RCS) of the rectangular conductors 38 a-h depictedin FIGS. 1-3. Similarly, the cross-sectional area of each of the roundconductors 40 a-f is substantially equal. The round conductors 40 a-fare aligned in a single row by the respective parallel sides 122, 124 ofthe core slots 112.

FIG. 6 shows an enlarged cross-sectional view of one of the core slots112 of the core 110 with the six round conductors 40 a-f positionedtherein. In the configuration shown, each conductor 40 a-f is separatedfrom neighboring conductors in the core slot 112 by at least oneinsulation layer 130 and from the core 110 by the insulation sleeve 121.The insulation layer 130 and the insulation sleeve 121 each have asubstantially uniform thickness. The diameter Ø of each of the roundconductors 40 a-f referred to herein includes the thickness of theinsulation layer 130. In the embodiment shown, the diameter Ø isapproximately 1.6 mm. As shown in FIG. 6, the insulation sleeve 121 ispositioned along the parallel sides 122, 124 and the core slot bottom128 so as to substantially surround the conductors 40 a-f in each of theslots 112 and thus defines a sleeve slot 132 with a sleeve slot widthW_(S) and a sleeve slot depth D_(S)′.

Since the diameter Ø of the round conductors 40 a-f is approximatelyequal to the width W_(RCS) of the rectangular conductors 38 a-h, thesleeve slot width W_(S) at the slot openings 26 can be the same for boththe cores 10 and 110. Similar to the core 10, the circumferentialspacing between the adjacent teeth 120 of core 110 may be consistentalong the depth D_(C) or the circumferential spacing may widen slightlyin the radial outward direction from the opening 26 to a width Wc of thecore slot 112 defined between the interfacing parallel sides 122, 124 ofthe circumferentially adjacent teeth 120. The stator winding may beprepared using any variation of a conventional technique suitable forround wire, and the round conductors 40 a-fh are inserted eitherindividually or as a group into their respective core slot 112 throughits opening 26.

When viewed along a cross-sectional plane situated perpendicular to thecentral axis 14, each core slot 112 and sleeve slot 132, and the commonopening 26 thereto are centrally positioned about the slot radialcenterline 34 (FIG. 5). The difference in the core slot width W_(C) andthe sleeve slot width W_(S) is substantially equivalent to twice thethickness t (i.e., 2t) of the insulation sleeve 121 that lines the coreslot 112 and defines the interior of the sleeve slot 132. The insulationsleeve 121 of FIGS. 5 and 6 is formed from the same material as theinsulation sleeve 21 of FIGS. 2 and 3. As such, the sleeve slot widthW_(S) is approximately equal to the slot width W_(C) minus two times thethickness t of the insulation sleeve 121 (i.e., W_(S)=Wc−2t), andapproximates the diameter Ø of the round conductors 40 a-f with similarclearances as were noted with the rectangular conductors 38 a-h. Thus, asingle file arrangement of the round conductors 40 a-f is maintainedalong the depth D_(S)′ of the sleeve slot 132 with circumferentialsurfaces of the arranged round conductors 40 a-f aligned along the slotradial centerline 34 and in abutment with one another.

As noted above, it is desirable to have about a 0.5 mm clearance fromthe circumferential inner surface 16 of core 110 to the innermostconductor in the radial outward direction (i.e., round conductor 40 a inFIGS. 5 and 6). To approximate this clearance in the core 110, thesleeve slot depth D_(S)′ (FIG. 6) is between N times the round wirediameter plus 0.2 ((N*wire diameter)+0.2) and N plus 1 times the roundwire diameter ((N+1)*wire diameter) where N=the number of wires in thecore slot 112. Thus, the relationship between the diameter Ø of theround conductors 40 a-h and the sleeve slot depth D_(S)′ can be statedas:

(N*wire diameter)+0.2≦D _(S)′≦(N+1)*wire diameter.

Thus, for the core 110 to be wound with a round conductor having adiameter of 1.6 mm with six conductors per slot, the sleeve slot depthD_(S)′ is between 9.8 mm ((6*1.6)+0.2) and 11.2 mm ((6+1)*1.6).Similarly, for the core 110 to wound with a round conductor having asmaller diameter, for example 1.3 mm, with fewer conductors per slot,for example 5 conductors per slot, the sleeve slot depth D_(S)′ isbetween 6.7 mm ((5*1.3)+0.2) and 7.8 mm ((5+1)*1.3). Based on thisrelationship, the core 110 including a round conductor with sixconductors per slot and a diameter that is approximately equal to thewidth of a rectangular conductor that can also be accommodated has asleeve slot depth D_(S)′ which is approximately 10% longer than thesleeve slot depth D_(S) in the core 10.

With this slot design, round wire can be inserted in a single row in thecore 110 and the slot fill factor will remain rather high atapproximately 0.56 (or 56% slot fill) (FIG. 6) as compared to the core10 with rectangular wire at approximately 0.62 (or 62% slot fill) (FIG.3). The slot fill factor of the core in the second configuration is 9.7%((0.62−0.56)/0.62)—or within 10%—of the slot fill factor of the core inthe first configuration. The slot fill factor in the embodimentdescribed is determined without deformation of the wires in the core byexternal force. Thus, the slot design of the core 110 provides a singlelamination design for two, separate stator designs: a high slot fillversion using round wire and a very high slot fill version using squarewire. As is known in the art, slot fill factor is equal to the ratio ofthe conductor area (or volume) over the total slot area (or volume). Forexample, a slot fill factor of 0.5 would signify that half (50%) of theslot area (or volume) is occupied by the conductors. The other half ofthe slot area (or volume) is occupied by conductor insulation, slotinsulation, and gaps in between the conductors and between theconductors and the slots sides.

FIG. 7 shows an overlay of the core 10 of FIG. 2 and the core 110 ofFIG. 5 with the core slot bottom 28 of the core 10 shown in phantomlines. As shown in FIG. 7, the relationship between the sleeve slotdepth D_(S) and the diameter of the round conductor established aboveresults in an elongation of the core slot 112 in the outer radialdirection. Specifically, the core slot bottom 28 of the core 10 isadjusted from the positioned depicted by the phantom lines to theposition of the core slot bottom 128 of the core 110. As discussedabove, the elongated core slots 112 enable the core 110 to accept bothrectangular conductors (i.e., 38 a-h shown in FIGS. 2 and 3) and roundconductors 40 a-f (i.e., 40 a-f shown in FIGS. 5 and 6) in alternativeapplications.

A flow diagram of a method 200 for forming stator assemblies forelectrical machines is shown in FIG. 8 and described with reference toFIGS. 2-6. The method begins by forming a plurality of identical statorcores including a first stator core 110 ₁ and a second stator core 110₂, each stator core 110 ₁, 110 ₂ defining a plurality of stator slots112 ₁, 112 ₂ spaced circumferentially about a central axis 14 of thecore and extending in a radial outward direction for a depth D_(S)′ froman inner circumferential surface 16 of the core to a core slot bottom128 ₁, 128 ₂ in accordance with the equation (N*wirediameter)+0.2≦D_(S)′≦(N+1)*wire diameter (block 202). In thisdescription of the method 200, subscripts are used after the referencenumbers to distinguish identical features of the first and second statorcores.

First windings 38 a-h are assembled on the first stator core 110 ₁ withthe first windings having a rectangular cross-section when viewed alonga cross-sectional plane situated perpendicular to the central axis 14 ofthe first core 110 ₁ (block 204). Second windings 40 a-f are assembledon the second stator core 110 ₂ with the second windings having a roundcross-section when viewed along a cross-sectional plane situatedperpendicular to the central axis 14 of the second core 110 ₂ (block206). The first windings 38 a-h are disposed in a single row within thefirst slots 112 ₁ of the first core 110 ₁, while the second windings 40a-f are disposed in a single row within the second slots 112 ₂ of thesecond core 110 ₂. An innermost conductor 38 a, 40 a of the respectivefirst and second windings 38 a-h, 40 a-f is spaced from the innercircumferential face 16 of the first and second core 110 ₁, 110 ₂ by apredetermined distance. The first stator core assembled with the firstwindings has a first slot fill factor and the second stator coreassembled with the second windings has a second slot fill factor. Thesecond slot fill factor is within 10% of the first slot fill factor.

The foregoing detailed description of one or more embodiments of thestator core has been presented herein by way of example only and notlimitation. It will be recognized that there are advantages to certainindividual features and functions described herein that may be obtainedwithout incorporating other features and functions described herein.Moreover, it will be recognized that various alternatives,modifications, variations, or improvements of the above-disclosedembodiments and other features and functions, or alternatives thereof,may be desirably combined into many other different embodiments, systemsor applications. Presently unforeseen or unanticipated alternatives,modifications, variations, or improvements therein may be subsequentlymade by those skilled in the art which are also intended to beencompassed by the appended claims. Therefore, the spirit and scope ofany appended claims should not be limited to the description of theembodiments contained herein.

1. A stator core for an electric machine, comprising: a core body (111)having a plurality of teeth (120), adjacent teeth (120) of the pluralityof teeth (120) defining respective slots (112) in the core body (111),each slot (112) having a slot depth (D_(C)′) in a respective direction(23) along which the teeth (120) extend from the core body (111) and aslot width (W_(C)) in a respective direction along which the teeth (120)are spaced circumferentially from each other, wherein the core body(111) has a configuration in which a plurality of elongate wire segments(40) having a round cross section are arranged in single file withineach slot (112), the round cross section having a diameter (Ø) thatapproximates the slot width (Wc), and wherein the slot depth (D_(C)′)has a range defined by the equation(N*Ø)+0.2≦D _(C)′≦(N+1)*Ø where N equals the number of the second wiresegments (40) in the slot (112) and Ø equals the diameter of the secondwire segments (40).
 2. The stator core of claim 1, wherein: theplurality of elongate wire segments are second elongate wire segments,and the configuration in which the plurality of second elongate wiresegments are arranged in a single file within each slot (111) is asecond configuration; and the core body (111) has an alternative firstconfiguration in which a first plurality of elongate wire segments (38)having a rectangular cross section are arranged in single file within ineach slot (112), the rectangular cross section having a cross-sectionaldimension (W_(RCS)) that approximates the slot width (Wc), and the corebody (111) in the first configuration has a first slot fill factor andthe core body (111) in the second configuration has a second slot fillfactor, the second slot fill factor within 10 percent of the first slotfill factor.
 3. The stator core of claim 1, wherein distal end faces ofthe plurality of teeth (120) define a circumferential face (16) of thecore body (111), and wherein a distal-most segment (40 a) of the secondwire segments (40) has a minimum clearance to the circumferential face(16).
 4. The stator core of claim 2, further comprising a plurality ofinsulation sleeves (121) arranged respectively in each of the slots(112), the insulation sleeves having a substantially uniform thickness(t), wherein the round cross section having a diameter (Ø) thatapproximates the slot width (W_(C)) more specifically approximates theslot width (W_(C)) minus twice the thickness (t) of the insulationsleeves (W_(C)−2t).
 5. The stator core of claim 4, wherein: the firstwire segments (38) have a first insulation layer (30) with asubstantially uniform thickness, the cross-sectional dimension (W_(RCS))of the first wire segments (38) including the thickness of the firstinsulation layer (30), and the second wire segments (40) have a secondinsulation layer (130) with a substantially uniform thickness, thediameter (Ø) of the second wire segments (40) including the thickness ofthe second insulation layer (130).
 6. The stator core of claim 5,wherein each insulation sleeve (121) defines a sleeve slot (132) with asleeve slot width (W_(S)) in the slot width direction and a sleeve slotdepth (D_(S)′) in the slot depth direction (23), wherein the sleeve slotwidth (W_(S)) is approximately equal to the slot width (W_(C)) minustwice the thickness (t) of the insulation sleeves (W_(C)−2t), andwherein the sleeve slot depth (D_(S)′) has a range defined by theequation(N*Ø)+0.2≦D _(S)′≦(N+1)*Ø.
 7. The stator core of claim 2, wherein thenumber of first wire segments (38) in each of the slots (112) is eightin the first configuration of the core body (111), and wherein thenumber of second wire segments (40) in each of the slots (112) is six inthe second configuration of the core body (111).
 8. The stator core ofclaim 7, wherein the first slot fill factor is 0.62 and the second slotfill factor is 0.56.
 9. The stator core of claim 3, wherein the minimumclearance of the distal-most segment (40 a) of the second wire segments(40) to the circumferential face (16) is 0.5 mm.
 10. Two stator coreassemblies for respective electric machines, comprising: a first statorcore (110 ₁) and a second stator core (110 ₂) that is identical to thefirst stator core (110 ₁), each stator core having a plurality of teeth(120) with adjacent teeth (120) of the plurality of teeth (120) definingrespective slots (112), wherein the first stator core (110 ₁) has afirst plurality of elongate wire segments (38) arranged in single filewithin in each slot (112), the first wire segments having a rectangularcross section, and wherein the second stator core (110 ₂) has a secondplurality of elongate wire segments (40) arranged in single file withineach slot (112), the second wire segments having a round cross section.11. The stator core assemblies of claim 10, wherein each slot (112) hasa slot depth (D_(C)′) in a respective direction (23) along which theteeth (120) extend from the respective stator cores, the slot depth(D_(C)′) having a range defined by the equation(N*Ø)+0.2≦D _(C)′≦(N+1)*Ø where N equals the number of the second wiresegments (40) in the slot (112) and Ø equals the diameter of the secondwire segments (40).
 12. The stator core assemblies of claim 10, wherein:each slot 112 has a slot width (W_(C)) in a respective direction alongwhich the teeth (120) are spaced circumferentially from each other, therectangular cross section of the first wire segments of the first statorcore has a cross-sectional dimension (W_(RCS)) that approximates theslot width (Wc), and the round cross section of the second wire segmentsof the second stator core has a diameter (Ø) that approximates the slotwidth (Wc).
 13. The stator core assemblies of claim 10, wherein the slotwidth (W_(C)) is configured to allow unrestricted radial insertion ofthe first wire segments (38) in the first stator core (110 ₁) and thesecond wire segments (40) in the second stator core (110 ₂).
 14. Thestator core assemblies of claim 10, wherein each tooth of the pluralityof teeth (120) has a distal end spaced from a bottom of the slot (112),and wherein a distal-most segment (40 a) of the second wire segments(40) in the second stator core (110 ₂) has a predetermined minimumclearance to the distal ends of the adjacent teeth (120).
 15. (canceled)16. A lamina for forming a core of an electric machine, comprising: alamina body (111) with a disk-like shape, the lamina body (111) having aplurality of teeth (120) with adjacent teeth (120) of the plurality ofteeth (120) defining respective slots (112), each slot (112) having aslot depth (IV) in a respective direction (23) along which the teeth(120) extend from the lamina body (111) and a slot width (W_(C)) in arespective direction along which the teeth (120) are spacedcircumferentially from each other, wherein the lamina body (111) isconfigured to accommodate a first plurality of elongate wire segments(38) having a rectangular cross section, the rectangular cross sectionhaving a cross-sectional dimension (W_(RCS)) that approximates the slotwidth (W_(C)) such that the slot (112) aligns the first wire segments(38) in single file within the slot (112), wherein the lamina body (111)is configured to alternatively accommodate a second plurality ofelongate wire segments (40) having a round cross section, the roundcross section having a diameter (Ø) that approximates the slot width(W_(C)) such that the slot (112) aligns the second wire segments (40) insingle file within the slot (112), and wherein the slot depth (D_(C)′)has a range defined by the equation(N*Ø)+0.2≦D _(C)′≦(N+1)*Ø where N equals the number of the second wiresegments (40) in the slot (112) and Ø equals the diameter (Ø) of thesecond wire segments (40).